The present invention relates to the field of fabric stretching and more particularly it relates to an edge-gripping system for stretching of fabric, especially art canvas, that is customarily stretched on a mounting frame with the fabric wrapped around the perimeter. The invention is directed to gripping the fabric in a manner that enables stretching along the gripped edges and thus enhances two-dimensional overall stretching both in original fabric mounting and later removal of the fabric from the frame for shipping and/or storage in rolled form, including subsequent re-mounting of the fabric, where the invention enables the fabric to be once more stretched onto the mounting frame in a satisfactory manner without degrading the fabric strength and integrity.
The term xe2x80x9cfabricxe2x80x9d as used herein is intended to include sheet materials of various types that may be deployed in artwork, billboards, posters and the like, particularly where the fabric is mounted by stretching it around the perimeter of the mounting frame as commonly practiced with canvas for paintings.
It is often required to stretch a sheet of fabric in two perpendicular dimensions either for pre-conditioning and/or priming or for stretching the fabric into place on a mounting frame such as the backboard or mounting frame of an art painting or an outdoor billboard. In many instances, at some time after the initial stretch-mounting there may be need for removal and possible re-deployment of the fabric: in known fabric-gripping systems, such rework is inherently troublesome and difficult, and often imposes a serious risk of damaging or destroying a work of art.
Large works of art stretched onto frames are very costly to ship and may even exceed the dimensional limits of the shipping company. It would be highly desirable to have a mounting system that enables uniform and efficient initial gripping and stretching of the fabric onto a frame, and that, unlike conventional gripping practice, allows the fabric to be conveniently removed at a later time, for example, to be rolled up for shipping or storing purposes to be later re-mounted to the frame.
For inexpensive artwork, the fabric, typically canvas, is traditionally gripped and stretched by hand over a fixed wooden frame and fastened to the wood frame with tacks, staples or adhesives while somehow being held under tension. Since the gripping, stretching and fastening must all be accomplished simultaneously, this requires a high level of skill that must be learned from trial and error experience; therefore the results vary from one operator to another and it is not unusual to encounter corner wrinkles in the finished products that are difficult to remedy, or even worse, corner tearing damage that causes major waste of raw fabric material and destruction of finished artwork.
In the conventional low-cost manner of fastening with tacks, staples or adhesives, there is generally no consideration given to later adjustment or removal, which, if required, is an extremely laborious and unsatisfactory operation. In one approach to mitigate this problem, staples are driven through a strip of material that is installed initially for the purpose of facilitating possible future removal of the staples if necessary; however each time this is done and the canvas is re-mounted, the fabric edge becomes further weakened by being punctured with a new set of staple holes in addition to the old unused set(s) of staple holes.
Stretching a rectangular sheet generally requires gripping the material along four edges and then applying stretching force in both lateral and longitudinal directions simultaneously; any uniform overall stretching that occurs involves expansion along each of the four edges, so the method of gripping must be able to expand accordingly to accommodate the edge stretching in order to avoid uneven stresses, distortion, corner wrinkles and tearing. Optimal stretching requires complex variations in the relative amount of tensioning force applied in the central regions of each edge versus the force applied near the corners.
In seeking to automate or at least mechanize the stretching, the method of gripping or clamping along each edge requires special attention to allow for the two-dimensional expansion. Anything added for thickening the edges of the material for gripping purposes must be able to expand along with the material, e.g. if a hem is sewn, even the thread stitches must be sufficiently expandable. Wedges, jamming strips, etc., whether inserted into a hem or merely forced into a groove with the fabric tend to act in a manner that constrains stretching along the edges and thus harms the uniformity and quality of overall stretching.
For mounting large and/or expensive canvas works there are available various adjustable frames that can telescope or otherwise expand in some manner in both dimensions toward or at the corners; this approach allows the fabric to be seized to the frame as a separate operation that can be completed prior to stretching. In some systems the tension can be released at a later time but demounting and remounting the fabric generally incur difficulties that range from problematic to impossible.
Typically known methods of gripping fail to adequately accommodate two dimensional stretching, fail to permit ready removal/remounting of the canvas, and/or fail to allow a removed canvas to be easily rolled up for shipping or storing purposes and then later re-mounted.
U.S. Pat. No. 5,113,611 discloses an expandable screen tensioning frame with expansion devices including telescoping corners, and provides descriptions of seventeen prior art patents directed to apparatus and methods for stretching fabrics.
U.S. Pat. No. 5,517,775 discloses a plastic edging strip that can be bent into a circle or around corners and is reinforced by thrust support brackets: fastening is by staples or other permanent fastenings into a solid wood frame or backboard. With no special provision for the two-dimensional stretching problem of corner wrinkles, this approach is shown as directed mainly to circular mounting frames which are inherently less prone to such problems.
Generally the above approaches and other that have been suggested for stretching canvas or other fabric material over a frame provide only for permanent attachment, and thus fail to provide capability of convenient subsequent removal from the frame at a future time.
It is a primary object of the present invention to provide an improved method and structure for two-dimensional stretching of material or fabric such as art canvas, particularly with regard to the manner of gripping the material for stretching.
It is a further object to provide an improved method and structure for gripping fabric such as art canvas for the purpose of mounting it stretched around the perimeter of a mounting frame in a manner that will, at a later time, permit convenient removal of the fabric from the frame as well as satisfactory subsequent remounting onto the frame.
It is a still further object that the system of gripping should allow the fabric, including artwork, to be readily removed from a frame and rolled up for shipping or storage and then later remounted and stretched onto the frame.
It is a further object that with canvas that has been processed, stretched and seasoned on a frame, that the system of the invention enable removal and remounting with accurate registration around the frame on the original fold lines.
The abovementioned objects have been accomplished by the present invention of a system of specially shaped gripping members that are attached to the material in a row along each edge in a manner that in co-operative engagement with the frame, accommodates two-dimensional stretching and also facilitates future dismounting of the material from the frame, rolling up for shipping or storage, and reassembly and re-stretching onto the frame.
The gripping members slide into the frame channels, the frame channels engage a mounting frame, then the fabric is stretched by expanding the frame. The members are made to slide freely in the frame channels and are spaced apart in a compliant manner that fully accommodates two-dimensional stretching of the fabric.
Openings may be provided in the frame channels to provide access to the members if necessary for optimizing the stretching operation.
The frame may be later adjusted to release the stretching forces and to enable the fabric, along with the gripping members, to be removed from the frame channels.
In a preferred embodiment, specially shaped individual gripping members are attached in pairs opposite each other on both sides of the fabric, and such pairs are arranged in a straight row near the edge of the fabric and permanently attached to each other through the fabric by fastenings such as wire staples or by hand or machine stitching.
In another embodiment a row of gripping members is formed in an automated process, joined together by curved flexible strips that allow longitudinal expansion and contraction to accommodate two-dimensional fabric stretching and that automatically set the spacing of the members.
In any embodiment, the gripping members are shaped and spaced apart in an optimal manner: close enough together to provide efficient gripping and yet far enough apart for the fabric to be rolled for transportation and shipping purposes, and then later re-stretched onto the frame.
Particular embodiments are disclosed with capability of mounting and stretching fabric around the perimeter of a fixed mounting frame.